The transversal equalizer is an electronic device which is widely employed in data sets (which transmit digital data over telephone lines) to equalize the amplitude response and envelope delay characteristics of the line. Reference is made to the article "Transversal Filters", Proc. of IRE, July 1940, pages 302 to 310, and to U.S. Pat. Nos. 3,292,110; 2,379,744; 2,719,270; 3,414,819; 3,368,168; 3,414,845 and 3,648,171, for a discussion and examples of such equalizers. In recent years transversal equalizers have been developed which are internally adjusted by closed loop control systems to provide automatic equalization for any telephone line to which the equalizer and the associated data set are connected.
Tranversal equalizers have been implemented using both analog and digital circuits. In analog implemented equalizers two basic electronic circuit components are characteristically employed, viz., tapped delay lines and voltage controlled attenuators. Typically, an eleven tap baseband equalizer, such as shown, for example, in U.S. Pat. No. 3,629,736, employs eleven or more voltage controlled attenuators and ten or more delay line sections. When such an equalizer is employed for line equalization the number of voltage controlled attenuators is doubled for each tap (see U.S. Pat. Nos. 3,400,332 and 3,727,136). It is these two circuit components, i.e., the delay lines and attenuators, which make up most of the hardware of automatic equalizers. Fully digital equalizers do not require these two circuit components but such digital equalizers are both large and expensive unless implemented with large scale MOS custom integrated circuits. Such digital equalizers typically employ ten bit words to represent voltage levels and use shift registers to provide the required delays. In such equalizers, the function of the voltage controlled attenuators is provided by fully digital multipliers. Reference is made to U.S. Pat. Nos. 3,633,014; 3,633,105; 3,651,376; and 3,699,321 for examples of digital transversal equalizers.